CRT electron gun with reduced stray electron flow between electrodes

ABSTRACT

A cathode ray tube comprising an electron gun. The electron gun has electrodes which are secured to supports by connecting elements. The width of the connecting elements varies. As a result, the high-voltage behavior of the cathode ray tube is improved.

BACKGROUND OF THE INVENTION

This invention relates to a cathode ray tube comprising a display screenand an electron gun having a means for generating electrons, a number ofelectrodes and a support which is composed of an insulating material,said electrodes being provided with connecting elements which aresecured in the support.

Cathode ray tubes are used, inter alia, in television receivers,computer monitors, oscilloscopes etc.

A cathode ray tube of the class mentioned in the opening paragraph is ofthe conventional type. The electron gun comprises a means for generatingelectrons, for example, a cathode. The electrodes are provided withconnecting elements which are pressed into the support. The support isgenerally made from glass which can be softened. In the manufacture ofthe electron gun, the electrodes of the electron gun are stacked on topof each other, whereafter the support is (or are, if more than onesupport is used) heated. By virtue thereof, the support and theprojections can be interconnected. This is generally achieved bypressing the support against the projections. Since the glass has beensoftened by heating, the connecting elements can be inserted into thesupport. The connecting elements may be integral with the electrode orthey may be secured to the electrode as a separate part. After cooling,the electrodes and the support are secured to each other.

In operation, voltages are applied to the electrodes. Due to saidvoltages, electro-optical fields are formed between the electrodes. Theelectrons generated are accelerated and focused by means of saidelectric fields. Ever higher demands are imposed on the quality of theelectron-optical fields. As a result thereof, the number of electrodesin the electron gun and the value of the applied voltages increase. Aproblem which arises is that sometimes the electrodes themselves cangenerate electrons. These electrons may hop between the electrodes. Dueto this, the cathode ray tube may be damaged, which leads to failure.Such electrons may also land on the display screen, thereby adverselyaffecting the contrast of the image displayed. These phenomena occur, inparticular, at locations where high voltages are applied to theelectrodes.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a cathode ray tube of thetype mentioned in the opening paragraph, in which one or more than oneof the above problems is reduced.

To this end, the cathode ray tube in accordance with the invention ischaracterized in that the electron gun comprises a pair of electrodeswhich are arranged one behind the other, said electrodes havingconnecting elements extending in a plane transverse to the electronbeam, the width of the connecting elements of one of the electrodes ofthe pair of electrodes differing from the width of the connectingelements of the other electrode of the pair of electrodes.

Hopping of electrons between two electrodes can be reduced by varyingthe width of the connecting elements. In well-known electron guns, theconnecting elements of successive electrodes are equal width.

The invention is, inter alia, based on the insight that electrons canreadily hop from one electrode to a proximate electrode via a connectingelement and to a connecting element of a nearby electrode via thesupport, and that in this process the edges the connecting elements forman important source of electrons. By making the widths of the connectingdifferent elements, the shortest distance, via the support, between theedge of connecting element of one electrode, and the next electrode isincreased.

In a preferred embodiment, the cathode ray tube comprises means forapplying voltages to the pair of electrodes, and the voltage applied tothe electrode having the widest connecting elements is lower than thevoltage applied to the electrode having the narrowest connectingelements.

In particular in this embodiment hopping of electrons is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be explained in greaterdetail by means of the accompanying drawing which shows a number ofexemplary embodiments of the invention.

In the drawing:

FIG. 1 is a partly perspective view of a cathode ray tube;

FIG. 2 is a partly perspective view of an electron gun;

FIGS. 3A and 3B are sectional views of a detail of an electron gun; and

FIG. 4 is a view of a detail of a further example of an electron gun.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Figures are diagrammatic. In the Figures, like parts generally bearlike reference numerals.

FIG. 1 is a partly perspective view of a cathode ray tube 1. Saidcathode ray tube 1 comprises an evacuated envelope 2 having a displaywindow 3, a cone 4 and a neck 5. In the neck there is provided anelectron gun 6 for generating, in this example, three electron beams 7,8 and 9. A luminescent display screen 10 which, in this example,comprises phosphor elements luminescing in red, green and blue issituated on the inside of the display window 3. On their way to thescreen 10, the electron beams 7, 8 and 9 are deflected across the screen10 by means of a deflection unit 11 which is located at the junctionbetween the neck and the cone, and pass through the shadow mask 12 whichcomprises a thin plate having apertures 13. The electron beams 7, 8 and9 pass through the apertures 13 at a small angle with respect to eachother and each electron beam impinges on phosphor elements of only onecolour. The means 14 for applying voltages to the electrodes of theelectron gun are also diagrammatically shown.

FIG. 2 is a diagrammatic, partly perspective view of an electron gun 6.Electron gun 6 comprises a common control electrode 21, also referred toas G₁. electrode, in which three cathodes 22, 23 and 24 are secured. TheG₁, electrode is secured to supports 26 by means of connecting elements25. Said supports are made of glass. An example of such supports are thesupports which are commonly referred to as “beading rods”. In thisexample, the electron gun 6 further comprises a common plate-shapedelectrode 27, also referred to as G₂ electrode, which is secured to thesupports by connecting elements 28. In this example, the electron gun 6comprises two supports 26. One of said supports is shown, the other issituated on the side of the electron gun 6 which is invisible in thisperspective view. The electron gun 6 further comprises the commonelectrodes 29 and 31 which are also secured to supports 26 by means ofconnecting elements (30 and 32, respectively). In this example, thesupports are secured on feed-through pins 35 by means of brackets 34.The electrical connections between the feed-through pins and theelectrodes are not shown.

FIGS. 3A and 3B are side views of a detail of the electron gun 6.Electrodes 36 and 37 are secured in the support 26 by means of securingelements 38 and 39. Said securing elements 38 and 39 are shown in detailin FIG. 3B. The width of the securing element 39 exceeds that ofsecuring element 38, for example 8 mm (securing element 39) and 5 mm(securing element 38). The distance between the electrodes (in thez-direction) is approximately 1.5 mm. In this example, the voltageapplied to electrode 37 is lower than the voltage applied to electrode36 during operation. Due to this, an electric field is generated betweenthe electrodes. This electric field may cause electrons to hop fromelectrode 37 to electrode 36. This phenomenon, in which the electronshop via the support 26, occurs in particular at the edges of thesecuring elements 39 of electrode 37. In cathode ray tubes in accordancewit the invention, this distance is greater than the distance betweenthe electrodes. In this example, the shortest distance between an edgeof securing element 39 and electrode 36, via the support 26, is 2.1 mm,which is more than the distance between the electrodes (=1.5 mm). Thisreduces the risk of electron hopping. FIG. 4 diagrammatically shows adetail of a further example of an electron gun for a cathode ray tube inaccordance with the invention. This electron gun comprises a stack of 4electrodes 41, 42, 43 and 44 having securing elements 41A, 42A, 43A and44A, respectively. In operation, voltages V₁, and V₂ (V₁ <V₂) areapplied to the electrodes, V₁, being applied to electrodes 41 and 43 andV₂ being applied to electrodes 42 and 44. The width of the connectingelements 41A and 43A is greater than the width of the connectingelements 42A and 44A. In this example, the widths are 8 mm (41A and 43A)and 5 mm (42A and 44A), respectively. Preferably, the difference inwidth between the connection elements is greater than the distancebetween the connecting elements, viewed along the electron beams.

Since the likelihood of electrons hopping between the connectingelements is substantially reduced or absent, damage to the electron gunor contrast reduction does not occur or is reduced in a cathode ray tubein accordance with the invention. A further advantage is that sparkingof the electron gun is enhanced. A customary step in the manufacture ofan electron gun is the sparking of the electrodes. To this end, veryhigh voltage differences between electrodes are generated. As a result,a flashover is generated between electrodes. By virtue thereof, burrsand loose particles are removed from the electrodes. Flashover betweenthe connecting elements during sparking has two adverse effects. First,flashover between the electrodes does not take place or is less likelyto take place and, second, loose particles can be formed. In a cathoderay tube in accordance with the invention, the risk of flashover betweenthe connecting elements is reduced.

It will be obvious that within the scope of the invention furthervariations are possible.

What is claimed is:
 1. A cathode ray tube comprising: a display screen and an electron gun having a means for generating an electron beam, a number of electrodes and a support means which is composed of an insulating material, said electrodes being provided with respective connecting elements which are secured in the support means, wherein the electron gun comprises a pair of electrodes which are arranged one behind the other, said electrodes having the connecting elements extending in a plane transverse to the electron beam, and wherein the width of said connecting elements of one of the electrodes of the pair of electrodes differs from the width of the connecting elements of the other electrode of the pair of electrodes; said cathode ray tube further comprising means for applying voltages to the pair of electrodes such that, in operation, the voltage applied to the electrode having the widest connecting elements is lower than the voltage applied to the electrode having the narrowest connecting elements.
 2. The cathode ray tube as claimed in claim 1 wherein said support means comprise first and second parallel arranged elongate support members extending parallel to a longitudinal axis of the electron gun.
 3. A cathode ray tube comprising: a display screen and an electron gun having a means for generating an electron beam, a number of electrodes and a support means which is composed of an insulating material, said electrodes being provided with respective connecting elements which are secured in the support means, wherein the electron gun comprises a pair of electrodes which are arranged one behind the other, said electrodes having the connecting elements extending in a plane transverse to the electron beam, and wherein the width of said connecting elements of one of the electrodes of the pair of electrodes differs from the width of the connecting elements of the other electrode of the pair of electrodes; wherein the difference in width between the connecting elements is greater than the distance between the connecting elements, viewed along the support means.
 4. A vacuum tube apparatus comprising: an evacuated envelope containing display means and an electron gun for generating an electron beam along a longitudinal axis of the electron gun, wherein said electron gun comprises; at least one support member made of an insulating material; first and second electrodes each including a connecting element secured in one of the at least one support member so as to mount said first and second electrodes in spaced apart relationship in the direction of the longitudinal axis of the electron gun, wherein the connecting elements extend in planes which are transverse to the electron beam and the connecting element of one of said first and second electrodes is wider than the connecting element of the other one of said first and second electrodes in a direction transverse to the electron beam; and means for applying respective voltages to the one electrode and the other one of said electrodes wherein the voltage applied to the one electrode having the wider connecting element is lower than the voltage applied to the other one of said electrodes which has the narrower connecting element.
 5. The vacuum tube apparatus as claimed in claim 4 wherein the distance from one transverse edge of the connecting element of the one electrode to the corresponding transverse edge of the connecting element of the other one of said electrodes is greater than the distance between said connecting elements in a direction parallel to the longitudinal axis.
 6. A vacuum tube apparatus comprising: an evacuated envelope containing display means and an electron gun for generating an electron beam along a longitudinal axis of the electron gun, wherein said electron gun comprises: at least one support member made of an insulating material; first and second electrodes each including a connecting element secured in one of the at least one support member so as to mount said first and second electrodes in spaced apart relationship in the direction of the longitudinal axis of the electron gun, wherein the connecting elements extend in planes which are transverse to the electron beam and the connecting element of one of said first and second electrodes is wider than the connecting element of the other one of said first and second electrodes in a direction transverse to the electron beam; wherein the difference in width between the connecting elements of the one and the other one of said first and second electrodes is greater than the spacing between the connecting elements viewed in a direction parallel to the longitudinal axis of the electron gun.
 7. A vacuum tube apparatus comprising: a. an evacuated envelope containing a display screen and an electron gun for generating an electron, said electron gun including first and second electrodes arranged along an axis; b. at least one insulating support member extending along said axis; c. at least one conductive connecting element extending from each of the first and second electrodes and having an end portion secured in the insulating support member, said end portion having a width defined by respective outer edges; each of said end portions being dimensioned and arranged such that the shortest distance via the insulating support member between any end portion outer edge conductively connected to the first electrode and any end portion outer edge conductively connected to the second electrode is larger than the axial distance between the respective end portions. 